Add Developer Certificate of Origin Text

We purposely chose to license Docker under the Apache 2.0 license. This is a well-known
license, which is popular for its permissive and flexible properties, while still
encouraging a collaborative community. It also makes certain representations with regard
to contributions, and the rights given to contributors, the project, people who use Docker,
people who modify Docker, etc.

This approach to contributions is inspired by the popular Linux Developer
"Certificate of Origin". This approach makes it simple for new contributors to get started,
and avoids bureaucracy in tracking contributions and contributors.

To indicate accordance, each individual contribution to the Project is signed off by the
developer, using his or her real name, email address, and github handle in the format below:

	Docker-DCO-1.0-Signed-off-by: Joe Smith <joe.smith@email.com>
Merged with master
hack/PACKAGERS.md: libdevmapper
Factor cache-probing logic out of buildfile.commit() and CmdRun().
Record added-tree sha256 in buildfile.CmdAdd, probe and use cache.
Add testcases for ADD caching, closes #880.
Add self to AUTHORS.
Add CHANGELOG.md entry for ADD caching.
Return meaningful error for meaningless Dockerfiles
add TestContainerOrphaning integration test
prevent orphan
Merge branch 'test-container-orphaning' of https://github.com/gabrtv/docker into prevent_orphan_deletion
discard test output
fix progressbar in docker push
Wrong HTTP method in events endpoint.
 Installation for FrugalWare
+ added missing link in index.rst
* some gramatic and spelling fixes

Thx jamtur :)
Fix glob expansion for no-cache setting.

On previous version, glob pattern will be expanded to actual file
names when writing setting to etc/apt/apt.conf.d/no-cache.

This patch fixes to quote to work cache clean command properly.
http method typo in documentation for events endpoint (all api versions)
docker-top: improve error message for non-running containers

Signed-off-by: Tzu-Jung Lee <roylee17@gmail.com>